Process for the manufacture of titanium dioxide



Patented Dec. 10, 1929 Iran FRITZ DOEBINCKEL, LEVERKUSEN-ON-THE-RHINE, AND LUDWIG MEHLER, OF DOBMAGEN-ON-THE-RHINE, GERMANY, ASSIGNORS, BY MESNE ASSIGNMENTS, TO TITKNIUM IIGMENT (30., INCL, OF NEW YORK, N. Y., A CORPORATION OF MAINE PROCESS FOR THE MANUFACTURE.OF TITANIUM DIOXIDE Ho Drawing. Application filed January 25, 1927, Serial No. 163,556, and in Germany February 1, 1926.

The present invention relates to the hydrolysis of titanium solutions for the manufacture of titanium dioxide which remains white on incandescence.

In themanufacture of white titanium dioxide, it is known to separate the same from iron by hydrolytic precipitation from a solution in which all the iron is present in the bivalent condition. When this separation is effected without taking particular precautions, titanic acid or a basic salt of titanium is nevertheless precipitated in a white form, yet

at incandescence it assumes a yellow to brown color caused by the small content of iron still contained in the same. I v In spite of this disadvantage, a titanium d1- oxide which remains permanently whitevat incandescence can be successfully obtained by effecting the reduction to such an extent that not only is all the iron reduced to the bivalent condition, but also' part of the titanium to the trivalent form, such for example as has been proposed in German Patents Nos. 152257 and 310304. However these processes involve the disadvantage that only the quadrivalent titanium is precipitated hydrolytically but not the trivalent, which latsay reducing agents for the manufacture of titanium dioxide, remaining white atincandescence, which do not convert quadrlvalent titanium into the trivalent form. These reducing agents are applied at least in such concentration that the quantity present not only corresponds to that required for reducing the trivalent iron, but that it must suflice to render innocuous the whole of the oxidizing agents present in the solution, inclusive of dissolved oxygen from the air. Furthermore care must be taken during the washing process following the hydrolysis that sufficient of said reducing agent must be present in order to prevent a re-oxidation of the iron. By the application of the method of working outlined-above, it is now possible to obtain a titanium dioxide, which remains absolutely white at incandescence, by the use of sulfurous acid.

The process can also be effected by first causing reduction to take place with a strong reducing agent which likewise attacks quadrivalent titanium-and allowing the reduction to proceed to such an extent, that the whole of the titanium still remains in the quadrivalent form, after which as above described a slight excess of a weaker reducing agent is added and maintained throughout the washing process. So long as the quantity proportions are known the addition of the reducing agents can be eflt'ected with equally good results eithersimultaneously or in any desired sequence.

We claim 1. In the manufacture of titanium dioxide which remains white at incandescence the step which comprises hydrolyzing a titanium solution in the presence of a reducing sulfuroxygen compound in a quantity corresponding at least to the trivalent iron and other oxidizing agents present in the solution.

2. In the manufacture of titanium dioxide which remains white at incandescence the step which comprises hydrolyzing a titanium sulfate solution in the presence of sodium sulfite in a quantitycorresponding at least to the trivalent iron and other oxidizing agents present in the solution.

In testimony whereof we have hereunto set our hands.

FRITZ DOERINCKEL. LUDWIG MEI-ILER. 

